{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"ab065ef807de8768a571e1f4787cc3b45e0c31dde2a4f17e2b2fe39ec28fdbce","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["4e501e591b80de7223db2d6ac0131568689664792eb00caa32cd9b7d340fc340","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"2f49c32b1cea59ff6f325bde3e7c9027b4396b58a1a35c49f6b0d40f1c9bfd2c","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"amo.electric-dipole-moments.neutron-edm","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Slow neutrons stored in a bottle precess in electric and magnetic fields, and a dipole would shift their precession rate when the electric field is flipped. No shift has yet been seen.","posed_since":"1950","precise":"The best bound is $\\left|d_n\\right| < 1.8 \\times 10^{-26}\\,e\\,\\mathrm{cm}$ (90% CL, PSI 2020) using ultracold neutrons with a Hg-199 comagnetometer. Determine whether $d_n$ is nonzero at the $10^{-27}\\,e\\,\\mathrm{cm}$ level, which corresponds to the QCD vacuum angle $\\left|\\theta_{\\mathrm{bar}}\\right|$ of order $10^{-11}$ (using $d_n$ of about $10^{-16}\\,\\theta_{\\mathrm{bar}}\\,e\\,\\mathrm{cm}$).","problem_ref":"4e501e591b80de7223db2d6ac0131568689664792eb00caa32cd9b7d340fc340","references":"","settled_by":"A neutron EDM measurement with total uncertainty near $10^{-27}$ e cm (n2EDM at PSI, or the US and Canadian ultracold-neutron efforts).","status_note":"The n2EDM apparatus at PSI was commissioned in 2024-2026 with its magnetic shielding and field uniformity characterized; no new limit as of mid-2026.","title":"Is the neutron EDM nonzero at the $10^{-27}$ e cm 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